1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method thereof, and more particularly to a liquid crystal display device in which a predetermined distance is held between a TFT substrate and a counter substrate by a support column system and a manufacturing method thereof.
2. Background Art
In a liquid crystal display device, liquid crystal is filled in a space formed between a TFT substrate on which pixel electrodes and thin film transistors (TFT) are formed and a counter substrate on which color filters and the like are formed, and images are formed by controlling molecules of the liquid crystal by an electric field. The distance (cell gap) between the TFT substrate and the counter substrate is extremely narrow, that is, several microns. Accordingly, proper setting of the distance between the TFT substrate and the counter substrate is extremely important for controlling transmissivity of light through the liquid crystal.
As an example of a method for setting a distance between a TFT substrate and a counter substrate, there has been known a method which distributes beads or the like in the space formed between the substrates. However, in distributing the beads in the space, the beads are distributed to regions where pixel electrodes are formed and hence, there arises a drawback that light is scattered in such portions thus lowering a contrast.
On the other hand, with respect to a conventional liquid crystal filling method, there has been developed a method in which a space defined between a TFT substrate and a counter substrate is sealed, an opening is formed in a portion of a sealing material, and liquid crystal is filled in the space through the opening, a method in which a necessary amount of liquid crystal is dropped on a TFT substrate and, thereafter, a counter substrate is adhered to the TFT substrate in a sealed manner thus sealing liquid crystal in the space, and the like. In any one of these methods, in distributing beads in the space, the beads move in the space at the time of dropping the liquid crystal into the space and hence, the number of beads becomes large in some places of the space and the number of beads becomes small in other places of the space. Further, the beads are also distributed into the inside of pixel regions where light emitted from a backlight passes thus actually lowering a numerical aperture of a liquid crystal display device or giving rise to a possibility of lowering of the numerical aperture of the liquid crystal display device.
As a method which defines a distance between the TFT substrate and the counter substrate, besides the above-mentioned example which makes use of the beads, there has been known a method which forms support columns formed of an organic film on the counter substrate (support column system). The support columns are mounted on portions of the counter substrate where the pixel electrodes are not present, that is, portions of the counter substrate through which light from the back light does not pass in general. Accordingly, there is no possibility that brightness (numerical aperture) is lowered due to the presence of the support columns. Further, the support columns are fixed to the counter substrate and hence, there is no possibility that the support columns move even when liquid crystal is dropped. Accordingly, the method which maintains the distance between the TFT substrate and the counter substrate using the support columns is also preferably applicable to a system which drops liquid crystal (liquid crystal dropping sealing system).
On the other hand, there has been known a COA (Color Filter on Array)-type liquid crystal display device which forms color filters on a TFT substrate. JP-A-2002-296615 (corresponding U.S. Pat. No. 6,816,222) (patent document 1) discloses such an example.
When the support column system is adopted by the COA-type liquid crystal display device, support columns are formed on a surface of a counter substrate on which a black matrix is formed, and the support columns are brought into contact with a TFT substrate on which color filters are formed. Here, to properly maintain a distance between the counter substrate and the TFT substrate, and also to prevent the support columns from slipping on a surface of the TFT substrate, pedestals which are brought into contact with the support columns are formed on the TFT substrate.